1. Field of the Invention PA1 a sensor, attached to an end of said manipulator along with an effector, for measuring an actual work path which leads in a path direction of said effector; PA1 memory means for storing predetermined taught data; and PA1 calculation means for managing information; PA1 calculating conversion information for converting a taught path to an actual work path by comparing actual work path information for sensing points obtained from measurement information of said sensor, and taught path information corresponding to said sensing points calculated from taught information generated by said taught data; PA1 calculating correction information for correcting the taught path to an actual work path using multiple sets of said conversion information obtained for each sensing; and PA1 correcting said taught information using said correction information. PA1 sequentially correcting movement instructions of said manipulator by storing predetermined taught data; PA1 measuring actual work path leading in a path direction of said effector; PA1 calculating correction information for correcting taught information based on multiple sets of measurement information; and PA1 correcting taught information generated from said taught data using correction information.
The present invention relates to a tracking apparatus and a tracking method for controlling the position and movement of a manipulator which holds an effector. More precisely, the present invention relates to an apparatus whereby an actual work path drawn on a workpiece is detected by a sensor, predetermined taught path data are amended with reference to the detected work path, and the effector held by the manipulator is drawn to exactly track the work path on the workpiece. The present invention also relates to a method for controlling the apparatus described above so that the effector exactly tracks the actual work path on the workpiece.
2. Relevant Art
The technology for controlling a manipulator for exactly tracking a work path is a crucial technology required for performing repetitive work in an environment wherein uncertainties exist. Therefore, many studies have been made in this field. Optical sensors are often used in combination with such technologies. For example, Hanada and Hanabusa studied, in "Spatial Curve Tracking of Industrial Robots", Measurement and Automatic Control, Vol. 16, No. 5, pp 126-132, 1980, the effects of sensor feedback. In the same document, they proposed a compensator for feedback control wherein predetermined work path data and off-line actual work path data are used.
Among various methods for tracking work paths, many working examples utilize predetermined taught path data. Recently, studies have been made on the methods wherein taught data are corrected with reference to the data obtained from optical sensors. One typical example is the study by Hirai and Shibata, "Detection and Control in Arc Welding", Welding Association, 1990. A method of amending a predetermined taught path is described in this document.
The methods described above have the object of solving a problem which may potentially be caused by the errors between the predetermined geometrical data of the path and the actual location of the path; such discrepancies are caused by errors in the orientation or dimensions of the workpiece. According to the methods described above, the position and angle of the effector are controlled by correcting the predetermined geometrical data of the path, position and angle of the effector, speed of movement of the effector, etc., with reference to the actual work piece. Optical sensors am employed to detect the actual location of the welding path on the workpiece and the position and movement of the manipulator are modified so that the welding rod traces the actual working path on the workpiece.
However the technologies described above have the following problems. According to the above-described technologies, detection data of the path are utilized in amending the position and movement of the manipulator. However, if the method is used in controlling welding rods for example, the detected optical information tends to include strong noise components which often lead to erroneous positioning of the manipulator.
Therefore, in a situation as described above, the reliability of the operation of manipulators is seriously degraded if the data from optical sensors are directly used in controlling the operation of the manipulator. If the correction of the taught path is wrong clue to errors in the measurement of the actual welding path, the actual path followed by the welding rod may substantially diverge from the corrected taught path.